Use the CPYTOIMPF “Copy To Import File” command to copy DB2 files to IFS files.
Is the app being migrated along with the data? Or are you just looking to decommission the app and store the data for historical reference? The CPYTOIMPF command is a way to put data into a .CSV (or other delimiter) format. There may be alternatives such as the Qshell db2 utility.
If the app itself is being migrated, then maybe something more like a JDBC extract would be appropriate. There might be ways to populate the new database more or less directly.