I have bought a serrisa bonsai. and at the beginning the bonsai was ok and doing well until the leaves started to get yellow and someone told me i gave it to much water. So i stoped/gave less it water. And now the earth is dry and the leaves are crimping. So i dont know what to do now. Could someone give me some advise.

Ps:as my name says it i am new to bonsai

Now the tree is dehydrated. That is way more serious condition than overwatered. All you can do now is getting the watering right. But do not expect miracles. Renovering from dehydration takes long time and sometimes fail.