A week after kicking 2.5 against St Kilda, Amiss was restricted to 0.1 from four disposals in Friday night's draw against Collingwood, with his only other set shot going out on the full.
It took his season tally to 14.15 from 10 games.
It's in stark contrast to his 41.17 from 22 games last season.
The 20-year-old is also struggling to cope with the increased physical pressure from opponents this season, leading to a dramatic drop in his output.
Longmuir has a simple message for the 20-year-old, who earned the nickname 'Nev Amiss' before even playing an AFL game due to his supreme accuracy.
"Do the reps. That's all you can do," Longmuir said.
"I don't think a lot has changed in his routine, he just needs to keep leaning in on his routine and get to work and practice."
Longmuir said there were plenty of people within the club willing to offer a helping hand, but he also doesn't want to overwhelm Amiss.
"He definitely is not getting left on his own," Longmuir said.
"(Forwards coach) Jaymie Graham is working with him, I'll have a chat with Jye. Sometimes you can have too many voices in situations like this.
"So everyone will want to help Jye and everyone will have some feedback for Jye, but he's proven to be a good goalkicker and a reliable set shot over a lot of years, including in his underage footy.
"He's got to trust himself."
Another aspect to come out of the game was Fremantle's over-reliance on handball at times, leading to numerous turnovers.
The Dockers pride themselves on being a high-handball team, but Longmuir felt they overdid it against Collingwood.
"I think that was as bad a handballing display as we've had all year," Longmuir said.
"In that last 10 minutes we actually trusted ourselves and our handball efficiency was a lot better.
"We're finding it hard at times to get the balance between using our numbers around the ball and trusting that our forwards are going to get it done.
"We should be growing a lot of confidence in our young forward line."
The draw left Fremantle with a 6-4-1 record ahead of next week's clash with Melbourne in Alice Springs.
