How to cancel pending transaction?

I have a pending withdrawal from my safex wallet that has been pending for a good two days now. How do I go about cancelling this withdrawal request?

You can’t be careful with tech man once you click it’s done be really careful I just lost 1000 verge last night from a mistaken click hard pill to swallow but a lesson none the less happy to learn it with a smaller amount rather than a bigger amount

You can’t cancel