I have iPhone 6s Plus iOS 13.7 , can’t update to iOS 15.7 help me

Itsjustruong wrote:

I did download iOS 15.7.3 but can’t installed it

Try a Forced Restart and then try the update again. As an alternative, likely not needed, turn Airplane Mode on and then turn Wi-Fi on, it should update just like mine do. And keep the phone connected to power as the Wi-Fi will otherwise disconnect while sleeping.

Here is a reply from Axel Foley, a well respected member of the Apple Community+ group, about updating without a SIM.

Update - Apple Community

Bob Timmons wrote:

The SIM card on your phone is missing.....therefore you have no cellular service. iOS will not update until you have a functional cellular connection.

Sorry, that is not correct. I have an iPhone SE 1st Gen which I use as an iPod to stream music and it has no SIM card. It is updated to 15.7.3 and I have had no issues with previous updates throughout the years. A SIM card is needed to activate the phone but once it is activated one is not needed. The iPhone will update through Wi-Fi. I normally keep the phone on airplane mode with Wi-Fi on, no issues whatsoever updating it. I also have an old iP7 and an old iP5, they update without a cellular connection to the max iOS allowed, 15.7.3 for the 7.

Try updating through a computer, Mac or PC.

Update your iPhone or iPad - Apple Support

Alternatively try a Forced Restart and then the update again

Force restart iPhone - Apple Support

The SIM card on your phone is missing.....therefore you have no cellular service. iOS will not update until you have a functional cellular connection.

Contact your carrier to get a new SIM card.