
Assuming it is the regular 1 dollar coin (weight 6.3 g), it is worth its nominal value of 1 Singapore dollar (about 0.75 USD, and it is still valid in Singapore).
If it is the commemorative dollar (weight 10 g), it should be part of a set. If in the original mint state, you may be able to get 2 USD for it.
A quick way to see if your coins have any value is to check https://www.NGCcoin.com/price-guide/world/. You can also look at prices for sold coins at Ebay (make sure to tick Sold Items).
If you still have questions about specific coins, do post them here. Make sure to include sharp and large pictures of both sides of the coin, cropped to show just the coin. Open a new thread for each coin, that is the best way to get answers.
How to post pictures