A puppy who scratches, freezes or hides after the collar goes on is not ready for you to ignore the response. Check the fit and the skin underneath. A collar that rubs, pinches or catches fur needs to be changed or removed safely. If the skin is sore or your puppy reacts painfully to neck touch, ask your vet.
Make sure the puppy is securely indoors before removing gear. For necessary outings, use a well-fitting, comfortable harness or another safe arrangement that meets local identification rules. Do not leave a collar or lead on an unsupervised puppy if it can catch on furniture or another dog's jaw.
Away from a real walk, let your puppy investigate the collar on the floor. Reward an easy look or sniff. Practise a brief touch around the neck separately, then the sound of the clasp at a comfortable distance. Only try fastening it when those steps are easy. Remove it before your puppy becomes worried and let them move away at any point. The everyday dog-handling guide can help with reward timing once fit and skin comfort are settled.
Today, check the skin and choose one calm, collar-free practice step. Your puppy does not need to wear discomfort to learn.
Sources: Dogs Trust on introducing wearable gear gradually. Dogs Trust on comfortable handling and choice.