I think it starts with knowing the sequence you are submitting. Is it a complete or partial gene? If you are not sure of what it is, you can refer back to the paper where you got the primers that you used to get that sequence. The other way is to blast your sequence and check for its pattern from the hits if it’s a well-documented organism.

Thanks Jacques Davy Ibaba i will check it first

use ORF finder

http://www.ncbi.nlm.nih.gov/gorf/gorf.html

I will use the Nucleotide accession ID from the paper the primer sequence was obtained as the reference ID for finding the nucleotide  or aminoacid sequences. This could be retrieved in a GenBank search using the reference ID.