Dest, 20, joined Barca from Ajax in a deal worth an initial €20 million at the start of the season and, due to an injury to Sergi Roberto, has been an ever-present since, making 21 appearances in all competitions.
He settled in quickly, impressing in October's Clasico defeat to Real Madrid, but said his form has tailed off over the last month, culminating with a thigh injury that forced him to miss two of Barca's last three matches.
"For me, it's important to get that confidence back because I feel a little bit unconfident right now," Dest told La Liga World.
"That's the most important thing for me right now: get the confidence back and play like I used to play and then I think I have a lot of potential."
Dest sat out the Spanish Supercopa semifinal win over Real Sociedad with a thigh problem and was substituted at half-time in the final last Sunday, a defeat to Athletic Bilbao, after rushing back too soon.
"Sergino has played a lot of games and this is just his first season with Barca," coach Ronald Koeman said in a news conference on Saturday.
"He's a very young player and it's complicated for the youngsters. He's been injured but he seems to have recovered and we will decide on Sunday if he starts or is on the bench.
"I hope he has no more problems with injuries, can get some rhythm back and provide competition."
Barca have now missed seven of 12 penalties taken this season and Koeman said the team had been practicing spot kicks on Friday and Saturday.
"We're analysing the issue with penalties because we've taken 12 this season and have missed seven, including the Supercopa shoot-out," Koeman added.
"That's a lot. It's too much. It's not acceptable. If Messi is not playing, who's the No. 1 taker, we need other players with the quality to score penalties.
"We've been working on them over the last two days. You can train for them just like you practice free-kicks. Of course, it's not the same in training as in a game when you're behind, but there are no fans, so there's no pressure."
Barca are unbeaten in eight league games and have risen to third in the table. However, they remain 10 points behind leaders Atletico Madrid, who also have a game in hand.