swap changed to a new partition, and so how to update that swap location?

Have Ubuntu Mate 18.04 and Mint 19.01 installed and I did some partitions changing which then changed the swap file from /dev/sdb5 to now /dev/sdb3 and so how do I make this correction so that swap is active again? If I can get the terminal commands to enter to fix this, thanks. I do know the file for this is in; /etc/fstab, but that is read only. With my 16 GB of memory in this computer, does Linux normally even use the swap file?