I have dual citizenship (USA& El Salvador). My income is from a Salvadorean company. I pay taxes in El Salvador. How can I get credit for this amount paid in El Salvador?

Did you live in USA or El Salvador during 2018 or was it partly in US and partly in  El Salvador?  How did you earn in El Salvador?

As a citizen of USA  you are taxed on world income no matter where earned.  Fo foreign earned income while  living in the USA ( i.e. tax home is USA ), any taxes paid to El Salvador is eligible for foreign tax credit or deduction if you itemize.  Tell me more about your situation.