Few things you must keep in mind before stepping ahead towards the process of resetting your iPhone like is your device completely charged or not and second, is having a backup of your previous data because it might be important to you.

Make sure that you have completed the process of backup.

Now, these mentioned steps to reset your iPhone:

• At, first tap setting
• Go to general setting

• Tap the option of reset
• Then select the option of erasing all content and setting.

watch this videos and follow the steps as shown to reset your iPhone. 

"hope it was helpful"