Clean it up, cut off all the loose bits, and put Eternabond on it. Then get a quote to properly replace the entire membrane.
Another vote for Eternabond. Dicor could be used for any complex-shaped spots where you are unsure whether the tape has a complete seal. I concur with assessing the overall membrane condition and possible replacement.
EternaBond RoofSeal White 4″ x50′ MicroSealant UV Stable Roof Seam Repair Tape | 35 mil Total Thickness | EB-RW040-50R – One-Step Durable, Waterproof and Airtight Repair https://smile.amazon.com/dp/B002RSIK4G/ref=cm_sw_r_cp_api_glt_i_0M2TNT6TN4QNDZBFYRJZ
Flex Seal has worked really conveniently for me
I’d probably go with dicor diseal sealing tape or patch. Then use some lap sealant around it if necessary but seems like just the tape would do what you need. You can get rolls of it
Rubber roofs only exist because we keep buying them.
Before you seal this up, you are going to want to inspect to make sure that there is no wet or dry rot underneath. It really looks like this has been exposed for a while.
