I have this column that I have created and and I wanted to change its type from multiple choice to an Yes/No option.
Unfortunately I don't see the option anymore.
It is not possible to change the field type of existing choice column to Yes/No(check box) in SharePoint.
You can change choice column to only below column types:
You can change Yes/No column to below column types:
For Indexed Error:
If you want remove the indexing on Yes/No column, then follow below steps: