Some learners assume it's important to ask their native friends for corrections. In my opinion it's unnecessary to get corrected by native speakers, and it's also a bad idea to rely on other people to correct your output. Most AJATTers who sound good never relied on corrections. Instead, they got many thousand hours of input and imitated native speakers through a technique called shadowing.
- If you haven't got enough immersion and can't output naturally yet, don't say anything. You're going to sound too bad, a native speaker won't be able to correct every mistake you make, and you won't be able benefit from the corrections. Without thousands of hours of input you can't reach a level required to understand, apply and learn from the corrections.
- If you've got enough immersion, you don't make a lot of mistakes, your Japanese is mostly correct, then when you accidentally make a mistake, you will know it. Your own language intuition and conceptual knowledge of Japanese will give you feedback. Much like in your native language when you accidentally say something stupid, you immediately know it.
- If you're not that good yet, and you're in a situation where you have to say something, but you don't know the correct way, your only option is to say what you can and assume it's incorrect. Later try to find a similar phrase in your immersion to check yourself and make a mental note.