If KRNL-Injector failed to find the Roblox process, delete KRNL App data and see. If that doesn't help follow the solutions mentioned in this post to resolve the issue.

Some other executors include: krnl, Fluxus, Script-Ware, Script-Ware M, and Synapse. Once the download is complete, install the Roblox Executor and open and log into it using your Roblox account.