Mark Hughes was relieved of his duties on Friday after leading the Rs to just four points from their opening 13 top-flight games.
And Redknapp accepted that he faces a big task as the Welshman's successor, but claimed the players must take some responsibility for the club's position.
"It's nice to be back. It's a big challenge and a tough job but a job I'm looking forward to doing," he told reporters.
"I've watched games on TV and I know the players and where they've been, so I've got a good idea of who's who. The lads I met yesterday were all upbeat. They've got to realise that they're in this position because they haven't performed to their capabilities.
"They've got to do better. They've lost a good manager in Mark [Hughes] but the players have to take responsibility for their performances. They've got to up their performance level and get us out of trouble. I feel there's enough ability for us to climb the table."
The former Tottenham boss went on to hail the west London club's owners and hinted at requiring their backing in the January transfer window.
"The owners have been fantastic. I don't know too many clubs that brought in more players than QPR in the summer. They couldn't have done anymore," he added.
|BOWEN DEFENDS HUGHES
|8/1||QPR are 8/1 with bet365 to beat Sunderland 1-0 in Harry Redknapp's first game in charge
"We're not overloaded with strikers. Bobby Zamora and Andrew Johnson are two good players to have missing, so that's certainly an area in which we're short. We'll have to wait and see. The window is a long way away and we've got a lot of games between then and now."
The 65-year-old was also not shy of warning his players about the work ethic he will require from them, claiming that those who do not graft will be shown the door.
"We've got to do better to give ourselves any opportunity to get out of this mess. We've all got to work hard - if they're not willing to work hard, they're not going to play," he continued.
"I need people who work - when you lose the ball, chase it. It's what you learnt in the playground. You chased after the ball if you lost. I need 11 people with ability who put effort in. If they do that, we've got a chance of surviving. If they don't, I'll find 11 who will."
The Englishman was in talks regarding the Ukraine national team job before being appointed by QPR and revealed just how close he was to taking on the role.
"Ukraine: It was a fantastic offer, they were great people. I met with them in London," he said.
"It was a great chance for me but in the end this came up and I decided the Premier League is where I wanted to be. But if this hadn't come up on Friday I would have gone, for sure."