Do you have unused disk (not allocated to a partition in use)? If so make a partition of a suitable size and make a filesystem on it. Copy what you want from /tmp/ into this new tmp and replace the old /tmp with the new one.
If you haven't got space like that you'd want to add disk or reduce the size of some existing partition.
Or if you had logical volumes rather than partitions the sizing is more flexible.
Or if you were using ZFS storage pools and had free space it should be easy to add some where you want it.