Help with .dat files on c550

[Guest pryddie]

hi

can anyone tell me where i can reset my phone as i have .dat files that look as though they have a bluetooth icon thingy by them, i understand that this was an error made by me when i clicked on them first it asked how to open them or something like that and i pressed the bluetooth thingy by mistake

how do i go back to get it to open with the correct one

thanks hope u understand this