An account number is shown below box 10 on Form 1099R and says see instructions. Where ?

The See Instructions is for the entity that issued your pension or retirement plan distribution 1099-R form.  It is not for the recipient.

If you are the issuer of the 1099-R, then click the IRS link below and view the Account Number instructions on Page 9.

https://www.irs.gov/pub/irs-pdf/i1099r.pdf