https://www.mangago.me/read-manga/heavenly_grand_archive_s_young_master/
https://www.mangago.me/read-manga/one_hit_teacher_master_baek/
https://www.mangago.me/read-manga/chronicles_of_the_demon_faction/
https://www.mangago.me/read-manga/youngest_son_of_the_namgung_clan/
https://www.mangago.me/read-manga/return_of_the_flowery_mountain_sect/
https://www.mangago.me/read-manga/nano_machine/ (the story is good, but I dropped it as it has romance and mc has two wives)
https://www.mangago.me/read-manga/the_return_of_the_crazy_demon/
https://www.mangago.me/read-manga/murim_login/
https://www.mangago.me/read-manga/chronicles_of_heavenly_demon/ (I don't remember if it's a reincarnation or not)
https://www.mangago.me/read-manga/i_reincarnated_as_the_crazed_heir/
Can you recommend an action story—preferably in a Murim setting—where the main character is either reincarnated as a weak or loser-type person, or sent back to the past when they were weak, and then becomes stronger or seeks revenge?