How can I file an EB-3 based 10-year green card when I already have an EB-5 based conditional green card?

This would not be possible as you are already a conditional permanent resident.

Since you are already a permanent resident, it is not possible to file to adjust status because that application must generally be from a nonimmigrant status. You can surrender your existing green card and then consular process your new green card application. However, that is especially tricky because getting consular appointments abroad at the moment is extremely difficult with so many backlogged cases.

As a conditional lawful permanent resident, you are not eligible to file I-485 adjustment of status. You will have to do immigrant visa processing at a U.S. embassy or consular office in your home country, where they will have you abandon your conditional green card so you may obtain the immigrant visa for your EB-3 case.

It is possible but complicated. You will need to abandon the conditional green card, get back in a nonimmigrant status if you want to adjust your consular process.

You would have to abandon your current EB-5 green card and apply under EB-3 since it is not possible to "switch" green card category.