I can walk BY myself. / I can go down the stairs BY myself. / I can go up the stairs BY myself. (a patient etc.) That reminds me OF something I heard before. / That reminds me OF something I saw before.

1. More typically: I can walk by myself. or I can walk on my own. 2 + 3 are fine. 4. That reminds me of something I heard before. 5. That reminds me of something I saw before.

The first three sentences are correct however, the second set of sentences should be "that reminds me of something I have heard before./ that reminds me of something I have seen before." Your version of "saw", while past tense, is not proper grammar.