If you've forgotten the codes to program your Nikai TV universal remote, there are several specialist sites online that can help you. Nikai is not a brand common in the Americas, and so doesn't have a dedicated customer service unit in the USA, but you could still try to email them here.
Nikai do however sell Grundig products, including the universal remote model GRC31588. If this is your remote, you can contact Grundig for assistance on +49 (0) 911-7030.
Elsewhere, you can download PDFs of Nikai remote manuals at manualpremium.com, while the general appliance and repair site fixya.com has a thread on Nikai universal remotes at fixya.com/support/t10168471-configure_uet_606_universal.
Other sites where you can download Nikai remote codes include tilevision.tv/doc/36 and download.yamaha.com/api.