hi i played the game in 2016 and left because my pc couldnt handle the game anymore, now i want to play it back, but i just dont remember anything what i need to know?

the problem i have is that my account is linked to my steam so i cant just delete it and start from the beginning wich is what i would like to do to understand eveeerything , but i also remember i had unlocked some prime equipment and characters from that year, not much but something, i remember frost prime, i dont want to lose what i got, maybe its important now and it was so costly to get him HAHA but i know anything, i dont remember anything and i just dont know what to do or understand anything from the story anymore