You can follow the process below to extend a USA business visa:
Step 1: Check if you are eligible for a B1 visa extension (must be physically present in the US on a valid B-1 visa)
Step 2: If yes, fill out Form I-539 (Application to Extend/Change Nonimmigrant Status)
Step 3: Arrange the documents required for a visa extension
Step 4: Complete the fee payment for visa extension
Step 5: Submit the visa application along with the documents and the fee payment receipt
Step 6: Wait for the status of your visa extension