I'm quite confused, when you say dash is low and bitcoin is high, are you referring to it's individual value in USD? If yes, the USD value of BTC doesn't matter. When you trade you choose a pair, for example DASH/BTC or vice versa. If you want to convert DASH to BTC, you aim for a higher BTC value of DASH.
DASH's BTC Value = Conversion Rate
So for example at the moment, the BTC value of dash is 0.00858640 based on coinmarketcap (Take note: the value will be different on coinpot)
When that value go higher, then you will have a higher conversion rate (DASH to BTC).
ex.
DASH BTC value ↑ (coversion rate) - 0.0087
DASH amount (you have) - 100
BTC you'll get - 0.87
When that value gets lower, then you will have a lower conversion rate (DASH to BTC).
ex.
DASH BTC value ↓ (coversion rate) - 0.0085
DASH amount (you have) - 100
BTC you'll get - 0.85
Btw, welcome to the forum