i assume you're referring to the sale of securities.
any items of type a - short-term or d - long-term (sales proceeds and basis reported to IRS which do not need to have their basis adjusted can be reported as single items. you will need to use the adjustment code of M - tells TT multiple transactions and to report on line 1a or 8a of schedule D and not on form 8949.
if there are still too many entries you can enter summary amounts for the other lines on form 8949 (no m) types/codes B, C, E, and F
then you need to prepare form 8453 checking the box 8949
https://www.irs.gov/pub/irs-pdf/f8453.pdf
If you are filing your tax return using an online provider, mail Form 8453 to the IRS within 3 business days after
you have received acknowledgement from your intermediate service provider and/or transmitter that the
IRS has accepted your electronically filed tax return. If you don’t receive an acknowledgement, you must contact your intermediate service provider and/or transmitter.
Mail Form 8453 to:
Internal Revenue Service
Attn: Shipping and Receiving, 0254
Receipt and Control Branch
Austin, TX 73344-0254
if you mail instead of e-filing your return just attach the sales detail to the return - don not use form 8453.
