With your drives plugged in, please run the following command and post the output. Copy the output as text, paste it into your reply, highlight it and click </> to format:
lsblk -fs
Also would be good to know what you added to /etc/fstab which didn’t work.
If you just want to mount your partitions on-demand in the file manager (and not automatically mounted at boot via fstab) please have a look at the following and try to see if that will resolve your issue: