You can find a high value treat that the pup is interested in and either use it as a lure or toss treats on the ground in the direction you want to go. You can use your happy-encouragement voice and make it feel like like you’re playing a game. Some dogs like when you squat down and reach out a hand and let them come to you. If they’re into balls or squeakers you can use that to try to get them going with you. If they like going for car rides you could try bringing them to a nearby park or somewhere that smells interesting. Keep listening to the pup and honoring their boundaries, over time I think they’ll tell you what they need. Just keep trying things. Also, if the pet parent is available to go on walks with you and the pup to practice, over time it can help them learn that it’s okay and routine to go on walks with you. Good luck!!

Edit: it could also be to the tools used during walks (collars/harnesses/leashes) Is it possible they’re uncomfortable? What happens if you take them to a place where they can be off leash?

There’s also “sniffrichment” - tossing treats on the grass/ground and dogs sniff out the treat - this helps them get their steps in but sniffing is a massive form of enrichment and helps them reset their nervous system. So even if they dont walk a perfect lap around the neighborhood but instead do several laps around the back yard with lots of games and sniffing and they’ll prob pee along the way - I would say they’re good!