The mission to make Knicks forward Kevin Knox better next season has begun.

Knicks coach David Fizdale revealed he spent all of last week with the Knicks’ 2018 lottery pick in the team’s Tarrytown facility working on elements of the 6-foot-9 forward’s game.

Fizdale had wanted the players to take three weeks off after the April 11 season finale, but said Knox got the bug to get back in the gym a week early.

“I don’t know if anyone’s been [back] in the gym in April,’’ Fizdale said Monday night in a guest appearance on MSG Network’s new talk show “MSG 150. “Kevin and I both had the itch and we got in the gym.”

Fizdale said “Fort Knox’’ originated innocently.

“We just started texting after one of the playoff games,’’ Fizdale said. “I told him in exit meetings, ‘Listen, I’m going to grab you most of the summer one-on-one.’ He was really up for that. So [I asked,] ‘What are you doing Monday?’ He said, ‘I’m free.’”

The 19-year-old Knox experienced ups and downs as the second-youngest player in the NBA — strength and defense the biggest issues. Fizdale, however, said he already noticed a new swagger last week.

“To his credit, he’s still in really solid shape,’’ Fizdale said. “But even in just in the week’s workouts, his walk is different. He has a little more confidence in him knowing what’s coming now instead of it being such a surprise to him.”

As the season got into March, Knox started to absorb contact better on forays to the rim. He finished the season averaging 12.8 points per game, but shot an inefficient 37 percent from the field. Knox rallied, however, to hit 40 percent of his 3-pointers in March and April. Fizdale felt Knox’s tutoring sessions with Knicks legend Bernard King have started to pay off.

“We really talked about building out his game, knowing his game,’’ Fizdale said. “How do I get to that place [on the court] and what do I do when I get there? A lot of that stuff are things we talked to Bernard King about — who’s real systematic how he scores. I think that connected with Kevin. So we kept building on that with the workouts and bringing intensity on every rep from start to finish. He really had a great week.’’

The Knicks’ disastrous 17-65 record will spawn a top-five pick in next month’s draft. Exactly where they will select is to be determined next Tuesday at the draft lottery.

During the offseason, Fizdale has run on a campaign preaching that despite posting the league’s worst record in his first year, a culture was built.

Asked to explain how that culture manifested itself, Fizdale said, “Our guys, with the way they stuck with it no matter what. You never saw them lay down. And you heard it in every interview, you never heard them go after each other.”

Fizdale survived, though his trademark black frames did not. They cracked during the season and Monday he unveiled new, dark camouflage-patterned glasses.

“I kick the record out the window,’’ Fizdale said. “It’s the first brick. If that’s what I had to sacrifice for the betterment of our group, so be it. I’ll take it for what I think is to come.”