How to rename username in Nextcloud

How does this play into the steps offered by @dolphinscorp ? What would the easiest series of steps be?

I’m having to consider this solution for about 7 users in my database. Trying to not over complicate the resolution. I should explain that for most all purposes I do not need to do this. My issue is that the structure of the username is causing these users to get kicked out of the Nextcloud Deck iOS app every time they open a card. I have traced it to be this as the only difference between them and the other users. These were users set up before I added LDAP. So they all have the underscore and random numbers behind their username.