Corolla E11 – V-belt squeaks

Hello people ! I have a corolla E11 ; built in 1997 ; 1.4 petroler. it is a liftback. have the 4E-FE motor. According to the toyota workshop, the timing belt and the belt were changed at approx. 100000 km. at the moment the car has 134000 km on it. but especially after the start, so if the engine is still cold and I let it run in the stand several seconds later, so that the engine oil is distributed and I then drive away, I notice already at half-entered gas pedal that squeaks a bit in the motor. sounds very much like a loose belt. what else can’t be. someone knows and knows someone with the motor, how to stretch the belt there so that this noise disappears? would help me very much !!! lg, marco