Hey there, Angelo! It's great to meet you. I thought this was an interesting thread, so I'm happy to help translate Rolando's videos. In his first video, he finger-spelled "disappoint." In his second video, he says that when you interpret to (American) sign language, "I will not let you down" changes to "ME NOT DISSAPOINT YOU." Similarly, the second portion of the video says "you not will let me down" changes to "YOU NOT DISAPPOINT ME" and he concludes by asking if you understand.
For PCGREER, adding more information... When interpreting, you should convey the overall meaning, and not sign it word-for-word in English. In this case, "letting someone down" is an English idiom, meaning to disappoint. It's also important to note that signs with the same handshape/location can have different meanings depending on context. Pointer finger to chin may also mean "miss," as in "I miss you," in other contexts.
Thanks!