Step 1: Download and install
Free download Aiseesoft 3GP Video Converter, install and launch it. Then the easy-to-use screen will pop up:

Step 2: Add files
Add the MKV files by clicking the "Add file" button.
Step 3: Select output format and destination
Choose the proper output folder and the profile "3GP" format.

Step 4: Convert
Click "Start" button to convert MKV to 3GP you can play the converted 3GP files on your portable mobile phone like Google Phone, BlackBerry…
Tip 1: Aiseesoft 3GP Video Converter software provides various advanced settings such as Bitrate, Encoder, Channels, etc. for seniors.

Tip 2: It provides the original video preview and output video preview to see the edited video effect when you manage it.
Tip 3: You can personalize the output effect in the Effect window such as Trim, Crop, Effect and more.
Why not have a try, you must be satisfied with this MKV to 3GP converter. Visit Convert MKV to 3GP for details.