The best thing you can do is to get a Yellow IInernational Vaccination book and have the hospital copy your details into that and stamp it. I faced the same problem since I was vaxxed with Astra Zeneca (Serum Institute if India) in Cambodia and when I moved to Europe last month, I had trouble since they had never seen a Cambodia Vaccination Certificate. The Yellow Book is recognized everywhere and it's a simple job to get the data transposed to that.
Of course as others have pointed out, it won't help much because Thailand is regarded by UK as a Red country and even if it was Amber, your vaccination would not be recognized as only EU/US cerrificates are accepted. I decided to get vaccinated again to ease my travels and am wating for my second Pfizer shot (on top of the two Astra Zeneca shots I had in Cambodia in March). No side effects after first Pfizer jab but double vaccination is not recommended by anyone at present.