Koinly allows you to change your cost-basis method for specific tax years, if you are using an xIFO method such as FIFO, LIFO or HIFO. It is not yet possible to switch to/from other cost-basis methods.

If you are using one of the xIFO cost-basis methods and want to change the method for a given tax year, simply open up your settings and select 'Add override', which is shown underneath your cost-basis method:

You can then set a different cost-basis method for any past or present tax years:

If you are unsure whether you are allowed to change your cost-basis method, then you should seek the advice of a licensed professional