Unable to extend rollback segment..... Help me to add space! ....

Dears,

First of all, I am sorry for this basic question but I have experience in 9,10 and 11 versions and I am struggling to add UNDO space to a 8.1.7.4 DB.

I get used to AUTOMATIC UNDO MANAGEMENT so I am not familiar with rollback segment.

The error is:

ORA-01562: failed to extend rollback segment number 2

ORA-01650: unable to extend rollback segment R1 by 2560 in tablespace RBS

Is it valid to add space to the tablespaces’ datafile? …. I tried it but other errors appeared, so the DB had to be bounce. I want to understand the correct steps if this happen again.