Lapsing happens automatically after 90 days of not progressing the Prospect, callbacks are not taken into account. Both the Account and the Case should be owned by the Lapsed Prospect user.
For a Sales user to adopt a Lapsed Prospect, they do this:
1) Search for the name of the company
2) Open the Case (not the Account)
3) Change the owner of the Case to them
The Account owner will be auto-updated, and then they own the Prospect.
There are a lot of requests for this from Sales, please send them the above so they can do it themselves.
If the Case and Account are not owned by the Lapsed Prospect user, or they are owned by different users, then you will need to use Admin privileges to help them adopt.