A SEP (land) class rating can be revalidated in one of two ways.
1) If you have flown 12 hours in the SECOND 12 months of the two year validity period of your rating (one of which needs to be flown with an instructor) then you just need to find an examiner to sign your Certificate of Experience. This needs to be done BEFORE the end of the two year period.
2) If you have not met these requirements, then you need to do a flight test with an examiner.
Because your C of E has expired, then you will need to do a flight test anyway.