Unfortunately, right now there is no solution to this problem, as the option to change the name card and give a nickname seems to have completely disappeared.
You could try closing the game and reopening it by running it as administrator, but this is not sure if it will work.
However, taking into account the popularity of this feature, we should have a solution available at any time, it is most likely that it will arrive for the update that is scheduled for June 9, 2021, so we will have to be pending.
That's all there is for now on how to fix the signature bug in Genshin Impact, so we hope the developers will bring us a solution for this issue as soon as possible.