How to gracefully leave a lab due to poor infrastructure and aiming to move into a new field of research?
Start interviewing now. When asked, explain your interest in changing fields and that your current postdoc is not a great fit for your new interests.
If your PhD advisor will write you a strong letter, having a letter from a job you only held for a couple months won't matter much. Likewise don't stick around to try to publish something unless you're very close. The most important thing you can do for your career is to get a job you like and will work for you ASAP. Losing a couple months is OK. Losing three years will torpedo you.