Here is a helpful IRS website for you: https://www.irs.gov/individuals/international-taxpayers/nonresident-spouse
How to Make the Choice
Attach a statement, signed by both spouses, to your joint return for the first tax year for which the choice applies. It should contain the following information:
A declaration that on the last day of the tax year, one spouse was neither a U.S. citizen nor a U.S. resident within the meaning of IRC section 7701(b)(1)(A) and the other spouse was and that you choose to be treated as U.S. residents for the entire tax year.
The name, address, and identification number of each spouse. (If one spouse died, include the name and address of the person making the choice for the deceased spouse.)
Regarding the foreign exchange rate:
https://www.irs.gov/individuals/international-taxpayers/yearly-average-currency-exchange-rates#:~:text=You must express the amounts,pay or accrue the item.