My son has developed a stutter, and I’m lost on how to help.

My son has developed a stutter, and I’m lost on how to help. My oldest is five, and over the last year has developed a pretty severe stutter. He is in school and has already started speech therapy. It breaks my heart watching him struggle to get his thoughts out. He gets so frustrated. I usually just wait with a smile for him to finish. Is there anything at home I can do to help him more? Thank you! Edit: Thank you all so much!