I had the same problem and the manual didnt help me. I noticed, that there is an old wallet version (8.7.0) on the first page of this ANN....and on their website it is 8.7.2.... When i used the wallet from their website instead, it worked and i was on the right chain again.
So my advice is to take the wallet from their website and do the bootstrap thingy to solve this issue
This worked for me as well. Upgraded from 8.7.0. to 8.7.2 on Mac from website wallet page https://espers.io/#download