Sonata automatic problem

Hello dear Hyundaians I have a problem with my 96 Sonata 2.0i 16V 102kw (139ps).The automatic transmission seems to be in the emergency run (remains in a gear), a little as if the “coupling” slips through. Reverse gear works perfectly. Has this happened to anyone before? What causes the control electronics to run emergency run? Converter damage? Solenoid valves clogged or broken? How do I get the machine out of the emergency run again? irepresent or can I do it myself? For example, do ignition on/off in a certain interval or battery depend for a certain time? Does someone here who prescribes or recommends Oel Hyundai at this machine? So enough questions for today, I hope it answers me one or a… Greetings to the forum