Stretch and RICE. Check your saddle position. If it persists see a physiotherapist for a diagnosis and an exercise programme
Rest ice compression elevation
sometimes get it myself .. Tendon over load to many miles
check your riding potion on the bike for starters
There are plenty of guides online, Shelton brown and you tube. Or you can pay for a bike fit. Are you new to rising, what bike do you have, is it new?
If it is tendinitis then you will need to let it completely heal before bike riding again or you will inflame it again. When I had it in my shin it took over 2 weeks before it healed completely.
would you not consider a independent bike fit ...
will aid you in the future !