Theres a few ways you can go about this.Using a file with a higher bit rate will allow it to be stretched further without distorting as much so try find a wav or flac version of the file you want to sample as opposed to an mp3.If you stretch a sample and then change the pitch back to the original then the sample can sound more distorted/tinny.
Welcome!This is a community focused on learning and improvement.Explore the wealth of and elsewhere before asking for help, do your own research. How To Change The Tempo Of A Sample In Fl Studio 20.