Reinstalling is good except if you have made settings that would make more than a hour to apply again.
But let's clarify @Blaz_Pivk, did you lost the password for your webconfig admin or the root as a user on the system? For the 2nd one, here is a great step-by-step guide how to recover root password on CentOS7. It will surely work on NethServer too.
For the 1st situation, I honestly don't know. Can you please report back about your results and sollution and share it with the community?