Rize Trade does not have a custom-symbol library or a settings screen to create symbols. Enter any symbol as free text on a manual trade, or put it in the Symbol column when you import with Custom CSV.
Manual entry
On the manual trade form, type the ticker or instrument into the Symbol field. For options, that field is labeled Underlying symbol. There is no preset list you have to pick from.
Custom CSV
When you import with Custom CSV, put the ticker or instrument in the required Symbol column. Custom CSV supports multiple asset types, so you can use the same column for the instruments you format in that file.