Many of the other languages on Duolingo use a computerized text-to-speech engine to read the exercises. That wasn't an option for Irish, and all of the exercises use recordings of an person reading the exercise. Slowing the TTS speech down just requires an additional parameter to be set, and while it is technically possible to slow audio recordings down, it would require additional software development and hardware resources, and it doesn't seem likely that the Duolingo engineers are likely to devote those resources to the languages that don't have a suitable TTS engine available.
So the short answer is no, Duolingo doesn't allow you to slow down the audio on the Irish course.
You might find the text-to-speech system at www.abair.ie useful, (it supports different speeds), though it has it's own issues.
I am also using Rosetta stone and it allows slowing speech. They have a voice app. So you can record and see if you are saying it correctly. They also have some lessons on sounds of letters. You have to pay but for me with a cochlear implant i need it. What i loke better anout this program is i can carry it with me on my phone I really like the vocabulary although i wish there were more pictures.
muinín means trust or confidence; it is commonly used in phrases to indicate that you have confidence (or faith or trust) in someone or something.
Tá muinín agam is the way to say "I have confidence" (or "I have trust", etc); it works the same way as saying something like tá cat agam meaning "I have a cat".
In English, when you say "I have confidence in ...", you use the preposition "in". It's a preposition, so it doesn't have to make sense, you just have to learn when to use it. In Irish, when you say tá muinín agam as ... you use the preposition as, so tá muinín agam asat means "I have confidence in you", or "I trust you".