Desktop app is stuck at indexing for days

I've done the rounds with the very unhelpful DB support people and have been referred to a specialist called Craig. He sent me the instructions below. I got to stage 7 and am stuck, as when I try to select the location I get an error that the location isn't available. DB support won't help 

I’ve taken a look at your account, and there appears to be some issues with the Dropbox software currently installed on your computer. To ensure that the software is working correctly, I’d like you to do a complete reinstall to try to fix the problem. This will not affect or remove the files in your Dropbox folder.
 
Please save and quit all programs accessing files in the Dropbox folder, and then follow these instructions:
 
Note: Please be sure to take note or take a screenshot of any Selective Sync settings you may have applied as well as the location of your Dropbox folder (if not in the default location) prior to re-installing, as you will need to match these settings upon re-install.
 
1) Stop Dropbox (If needed):

·       Click the Dropbox icon in the menu bar at the top of your screen

·       Click on your profile picture or initials to the right of the search bar and select 'Quit Dropbox'

 
2) Download the newest version:
 
https://www.dropbox.com/downloading
 
3) Open your Terminal app (Located at /Applications/Utilities/Terminal)
 
4) Copy and paste the following lines into the Terminal, ONE AT A TIME, and press ENTER after each one. PLEASE make sure you copy and paste these commands (don't type them by hand), as getting them wrong could cause some harm. You'll be prompted for your computer's admin password (not your Dropbox password) after entering the first command. Keep in mind that the password field in the terminal will remain blank as you type your password. After you type it, just press ENTER. You'll know that these instructions complete normally once the initial line of text (called prompt) comes up again:
 
sudo chown "$USER" "$HOME"
sudo chown -R "$USER" /Users/racheltaylor/Library/CloudStorage/Dropbox
sudo chmod -R u+rw /Users/racheltaylor/Library/CloudStorage/Dropbox
sudo mv ~/.dropbox ~/.Trash/dropbox.old
sudo chmod -N ~
sudo mv /Library/DropboxHelperTools ~/DropboxHelperTools.old
 
Please note that once the prompt displays, the instruction completed the requested task and is ready for the next command. If the command returns an error or does not respond after an hour, you may want to try restarting your computer and try these steps again.
 
5) Delete the Dropbox application from the Applications folder. You may need to provide your computer password in order to perform this action.
 
6) Open the .dmg file from step # 2 and double click the Dropbox icon to install Dropbox.
 
7) When Dropbox has finished installing, during the initial setup and sign in process, apply any Selective Sync settings you may have had prior to the reinstall and select the Dropbox folder location (if not in the default location).
 
IMPORTANT NOTE: Because this process removes the previous settings and configuration, if you wish to avoid re-downloading your Dropbox content, you will need to manually choose the location for Dropbox to sync to, otherwise you will create a new Dropbox folder which will start to download your content again.
 
To select your already established folder on your drive, after signing in and choosing which folders to sync, and before you click on "Open my Dropbox folder", you should see an "Advanced Settings" link, click on this.
 
Then you can choose the parent folder of the already established Dropbox folder. For example, if you have your Dropbox folder in the path "/Volumes/DifferentPlace/Dropbox (Team)" you'll want to select the folder "/Volumes/DifferentPlace/".
 
At the end of this process, after clicking "Open my Dropbox folder", it might take some time to re-index the files and sync any pending changes.
 
Please note that any changes made to the files in the Dropbox folder, the web interface or other linked devices while the folder was "off-line", will generate conflicted copies:
https://www.dropbox.com/help/36
 
Finally, this process only works when linking to the exact same account that was previously linked to this computer. If you'd like to merge accounts, please refer to the following Help Center article:
https://www.dropbox.com/help/9104