Copy the link and open the app. Tap the button on the top right, and choose the option in the middle

You can use #[3]​‘s as an example

https://simplex.chat/contact#/?v=1-2&smp=smp%3A%2F%2FSkIkI6EPd2D63F4xFKfHk7I1UGZVNn6k1QWZ5rcyr6w%3D%40smp9.simplex.im%2FHwpFF5Y2Ik39E3HFx3hWqGf-LCrSznle%23%2F%3Fv%3D1-2%26dh%3DMCowBQYDK2VuAyEAJWgXS_bqRfnjLSEQaT-CkialkYdsbBdbW2P-XlIGf3I%253D%26srv%3Djssqzccmrcws6bhmn77vgmhfjmhwlyr3u7puw4erkyoosywgl67slqqd.onion