imo, it's best to use larger diameter serving rather than build up the string fiber or existing serving. if yer a split finger shooter, the nock to serving fit MUST be loose. with 8 strands of dyneema for all my bowstrings, a ,019" halo center serving yields a nice loose fit for carbon and woodie arrow nocks.
if one must build up the string, my preferred method is to wrap the center serving nock area only with flat dental floss, lock down with water thin cya, serve over the string and floss, add a tie-on nocking point and coat the knotted point with thin cya. quality, water thin cya is purchased from hobby shops (hot stuff, jett, whatever - they're all good). use that cya to lock down serving ends, 'y' yokes for endless loops and flemish braids, and lotsa other archery tasks.
ymmv.