due to covid, I think I will not be able to meet him in person. Writing him an email is the only option. In the email, should I introduce again to him who I am? He already knew and remembered my name. Could you please tell me a format I could use?
In my experiences, emails are a formal kind of communication, so it shouldn't hurt to compose and format formally.
Depending on how well you know each other, the "introduction" can be as long as an attached curriculum vitae or as short as a line of "I am Jon Doe".
If you've contacted that person in just a month and a half (which is quite short), you can go brief in this part and just say "I'm Jon Doe" and continue on describing your desires (tell them you want a reference letter). Try to correctly evaluate their familiarity with you - not every professor remembers their course students that well, in which case you may still want to include more details, up to a complete copy of your CV.
In addition, for these kinds of emails (requesting work or help from others), I prefer to err on the side of safety by being professional.
The last time I asked a professor for a recommendation letter around half a year ago, in a very similar situation to you. I attended courses from this professor and participated in contests and won good prizes (where all teammates were MSc students in his lab). I had not worked in research projects in his lab. I ended up writing my request email like this:
Dear Prof. Jon Doe,
I am iBug. I'm applying for a plumber at Super Mario Bro's Institution and I'm looking for a referral letter.
I attended your courses [course A] and [course B] and received grades of A+ and A, respectively. I also took part in [example competition] in a team and won the 1st prize. My full CV is attached in this email, too.
I'd be very glad if you can write a letter for me. I'm looking forward to hearing from you.
Be sure to change specific wording / sentences according to your situations.