Start small
Warm weather can change how much activity feels comfortable for a dog.
There is no need to rush. A predictable, manageable step is usually more useful than trying to solve the whole situation in one day.
Try this next
Plan walks for cooler times, offer shade and water, and stop if your dog seems distressed or overheated.
Notice what helps your dog stay comfortable and engaged, then repeat that version before making the situation harder.
Keep it kind and practical
Keep the next step easy enough that your dog can succeed. If you are worried about safety or feel stuck, pause and ask a qualified reward-based professional for help.