If you have an LAPL then you do not have an SEP Rating as these cannot be entered in to an LAPL.
It is the Licence (LAPL) itself that would entitle you to fly SEP aircraft (to LAPL privileges) and the Licence is valid for life.
There is nothing for you to Renew or Revalidate.
However, as well as having a valid medical; before each, and every, flight it is your responsibility to ensure you meet the Recency Requirements in order to exercise those privileges.
FCL.140.A LAPL(A) — Recency requirements
(a) Holders of an LAPL(A) shall only exercise the privileges of their licence when they have completed, in the last 24 months, as pilots of aeroplanes or TMG:
- (1) at least 12 hours of flight time as PIC, including 12 take-offs and landings; and
- (2) refresher training of at least 1 hour of total flight time with an instructor.
Any PIC, or DUAL, flying you have done in an SEP can count - you just need to check your Log Book to always make sure they fall within the two years prior to any flight.