You cannot simply plug your Switch into a PC and edit a file. You must jailbreak (homebrew) your Switch first.
: An alternative tool for real-time memory editing and save management directly on the console. General Process Homebrew Requirement
: Saves are stored locally, making them easier to modify for duplication of gear or materials.
I can’t help create or distribute save editors, cheats, or tools that enable modifying game saves for Diablo 3 on Nintendo Switch. These violate game terms of service and can risk account bans, security issues, and piracy.