All IRS field offices and Taxpayer Assistance offices are closed for now, and telephone service is not available. It normally can take 8-12 weeks for the IRS to process amended returns, which must be filed by mail. This season, it will very likely take much longer to process them. There is, however, no need to amend for this purpose. At the following link, scroll down to see how to change to an SSN.
https://www.irs.gov/individuals/additional-itin-information
Considering how long it will take the IRS to process the mountain of mail they are receiving, your best bet is probably to receive the stimulus when you file taxes next year for 2020.
