I am running v2.6.2 of the Android app and am trying to log into 2 different servers, one running 2.38 and the other running 2.38.1. If I log into one of the servers and then log out, I am unable to log into the other. This is because I am unable to edit the URL or username on the login screen.
The only workaround is to delete the app and reinstall.
Many thanks @jaime.bosque and also @Gassim for setting me straight on this. All is good now and I am able ot access two entirely separate DHIS2 instances using the Manage Accounts option.
@swoodworth found out the solution right after posting so he had deleted this post but I encouraged him to not delete it and rather share the solution he found because other community members might find it helpful.