500PCS 0.7mm Watch Gasket, Water Proofing Rubber O Rings for Watches Back Covers, Watch Parts for Watches Repairs (31mm - 40mm)

Order something like this: https://www.amazon.com/dp/B0F9NQS2RQ/?coliid=I1Y2WA10VWPZ27&colid=111HD6PPIQ5CK&psc=1&ref_=list_c_wl_lv_ov_lig_dp_it and use whichever fits. If they're all too big, there's a similar set that is all the sizes 30mm and below.