How do I convert Micro Focus ORGANIZATION RELATIVE files to isCOBOL format?

If the relative file's records are fixed-length, you do not need to do anything to them, isCOBOL will read them as-is.

Variable-length relative files must be converted to fixed-length relative files.
Use a Micro Focus program to do this conversion, reading from the variable-length file and writing to a fixed-length file using the maximum record size as the record size of the output file.

Here's why:
In Micro Focus COBOL, the format of an ORGANIZATION RELATIVE file with fixed-length records is the same as that of an ORGANIZATION BINARY SEQUENTIAL file with fixed-length records, except that each record has appended to it a two-byte marker that has the value X"0D0A" if the record exists and X"0D00" if the record has been deleted.
If the file has variable-length records the format is similar except that each record is preceded by a two-byte record size, then padded with low-values to the maximum size, and followed by the two-byte marker.

In isCOBOL, the record storage format for relative files does not include two-byte record-size indicators or record-deleted markers.
Instead, the records are stored consecutively including only the record data. If necessary, each record is padded with low-values to the maximum size.

isCOBOL marks deleted records in the file by replacing the record data with all low-values.
Therefore writing a record containing all low-values from COBOL will cause that record to appear to be deleted.