For a few years, I've had Linux Mint installed on a 50GB partition on my 2015 MacBook Pro. Today, I decided to remove the installation (I needed the extra 50GB and wasn't using Linux Mint anyway) and used Disk Utility to erase the 50GB partition. After rebooting, I was brought into a minimal GRUB at startup. Rebooting a second time (this time while holding the Option key), there was only an EFI boot option. I decided to go into Internet Recovery mode (using Option Command R) and tried to do a fresh install of MacOS. However, the only partition that was available to install MacOS on was the 50GB partition that I had previously erased.
As it currently stands, my laptop is booting from the 50GB partition (while the other 450GB that had my old MacOS installation cannot be accessed anymore). How would I go about accessing my old MacOS installation and recovering the (hopefully not lost) files?