A wretched campaign full of poor decisions meant Saints knew their 11-year stay in the Premier League was over with two games to spare.
Southampton are on a winless 12-match run and have lost their last five on the bounce, with Swansea boss Russell Martin lined up as manager as they prepare for life in the Championship.
Selles hopes his last match in charge ends with a positive result on Sunday, which could also see homegrown skipper James Ward-Prowse make an emotional farewell.
“I think you need to choose in which mode you are every day,” Selles said of the atmosphere at St Mary’s on Sunday. “I think the fans need to do the same.
“I know, I understand the disappointment of the season but, as you say, it can be the sun shining and then a big opponent, last game in St Mary’s in the Premier League this year.
“We will not have for at least one more year and I think it’s a good opportunity to go on a journey together and try to make a good football match.
“I thank our fans for being supportive in one of the hardest seasons that they had in the last 12 years.
“Hopefully we can have a good environment on Sunday and then we can make something together.”
“It’s always a tricky question because I know Jurgen (Klopp) said that he will make some changes in the line-up probably,” he said.
“It’s a situation with less pressure than if they were playing from the Champions League, of course.
“But sometimes less pressure means more freedom and sometimes more freedom (helps), and they can go in both directions, so it’s just a different game.”
But there could be some positives to hold onto, with teenagers Kamari Doyle and Dom Ballard pushing for game time after making their league debuts last weekend.
Talented full-back Tino Livramento could also get some time off the bench after ending his 392-day injury lay-off when coming on for 20 minutes at Brighton.
“Tino will not play from the start due to his time restriction,” Selles said.
“He can play at least the same amount of minutes as he did against Brighton.”