As I replied to the same question you posed on another PPRuNe forum
, you need to fly some refresher training in a SEP Class aeroplane, then take the LST for a SEP Class Rating renewal. Much the same profile as an LPC, but a different emphasis by the Examiner.
These days it also includes an element of VFR navigation. As in proper navigation, not map reading and track crawling.
Next year you will need to have your licence re-issued.