The fields and records in exchange files are separated by specific characters dependent on the exchange format. If you want to import an exchange file that is just like one of the formats that Designer can import, but has different separator characters, you can just change the separators for that format. (You don't need to specify separator characters if the ones used in the exchange file are the default characters as specified for the relevant format.)
If you have a file structured like for instance an ASCII delimited one, but in which the field separators are not commas but some other character, you can still import it as an ASCII delimited file; then it's necessary though to specify the field separator used in this file. In the tag mapping in an import job, you include <FS> as a destination tag. For the source tag you provide either the hexadecimal ASCII value of the field separator character, or just the character itself when it is printable.

Example of a tag pair in which a TAB (a non-printable character) is specified as a field separator:

(Hexadecimal values start with 0x.)

Example of a tag pair in which a semicolon is specified as a field separator:

 

You can also specify a record separator this way (only required if it deviates from the default record separator for the exchange file format), but now use <RS> as destination tag. In (Adlib) Tagged files for instance, the default record separator is **, but when you have a similar file to import, that separates records with say, only one *, you can specify this in the tag mapping: