The only time a 'crash' (which is defined as a 40% drop by the way) matters is if it happens less than about 5 years from when you actually need to start drawing the money. Investments should be viewed over a 10 year period. If it's more than 10 years till your retirement date then during and immediately after a crash is probably the best time to invest - you get more for your money. If it's less than 10 years you should probably be selling the higher risk stuff and concentrating on UK bases gilts and bonds. These will be much less volatile, but give much lower growth (there are other stratergies but de-risking is probably best for a novice investor).
Day to day week to week or month to month variations of +/-5% shouldn't concern you. If they do, then you've invested above your true risk profile. We've been in a bull market for about 10 years (till Feb/March 2020) so anyone who has only started investing in that time has only known the good times which has probably lead to a lot of people investing well above their risk level. Then when the CV19 problems hit, the markets drop, and the punters panic and sell - crystallising their losses. Don't.
Most of my investments are back to their Jan 2020 levels now. And some of the stuff I bought in Feb/March is 50% up.