United endured their worst season in Premier League history with their lowest points tally (58) in the competition's era and failed to qualify for next season's Champions League.
Despite their disappointing campaign, Ronaldo said he is looking forward to being successful next season and helping the club return to "where they belong."
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"I was happy of course to be back at a club that really raised my career. So it was unbelievable," he told the club's official website on Friday.
"The feeling when I [came] back again, it was nice to feel the supporters. The happiness of them as great. I was -- and still am -- very happy to be here."
He added: "It's still my motivation to carry on working hard, to still love the passion for the game, and of course Manchester and my teammates help me all the way so I have to appreciate all the people who help Cristiano.
"But the most important thing for me is to try to win the games and try to win some championship or some cup but I believe that Manchester will be where they belong. Sometimes it takes time, but I still believe."
Ronaldo enjoyed an impressive return to Old Trafford with 24 goals in all competitions and was nominated for the English Professional Footballers Association Player of the Year award.
New manager Ten Hag arrives to United after winning three league titles with Ajax and Ronaldo said the Dutchman needs time to achieve success in England.
"I know he did a fantastic job for Ajax and that he's an experienced coach," Ronaldo added. "But we need to give him time and things need to change -- the way he wants.
"I hope we have success of course. Because if you have success, all of Manchester are going to have success as well.
"So I wish him the best. We are happy and excited -- not only the players but the supporters as well. I wish him the best and let's hope that next year we're going to win trophies."