How to change shortcut for switching chrome tabs

You change it in App Shortcuts, at the bottom of that window.

However, before you do, check the appropriate menu item for next/prev tab - Chrome usually defaults to Ctrl ⌃ Tab ⇥ & Ctrl ⌃ Shift ⇧ Tab ⇥

The Cmd ⌘ Opt ⌥ → / ← is an unpublished alternative.

If you do want to change it, then select App Shortcuts. If there's no entry there for Chrome already, press the + at the bottom, select chrome in the list, type the exact name of the command you wish to change, then add the command. [If it exists in the list, then just select it before pressing +
It will immediately reflect your changes. Revert to defaults by deleting the entry.