How can I use my iPhone again

Who repaired your phone, take it back to them and have them fix it.

They might have removed your SIM card or given you a different phone that is tied to a different carrier than yours.

surya124 Said:

"how I can use again cellular : Please I request with apple team to solve my problem how can I get phone again to use all service I'm forgot my passcode then I give to repair but he did bypass my phone after bypass I can't use my cellular & update my iPhone 6 Plus"

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"No Service":

I see that "No Service" shown on the top-left corner of your screenshot that was there. So, go here: If you See No Service or Searching on your iPhone or iPad - Apple Support

Screenshot:

surya124 Said:

"Dear , sir Now what can I do how can I get my phone in good condition please give me few solution"

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To Check for Updates:

Seeing the black-rainbow emblem, per se', Wi-Fi seems to be up and running. So, try updating via the following:

Use a Computer and Ethernet:

Start with attempting an update through use of a computer. If you cannot use Wi-Fi, then use Ethernet.  Go Here: Update your iPhone Using a Computer - User Tip. On the computer, you would connect it through Ethernet, going directly into your router. For a Mac (or PC) that does not have Ethernet, this would be the adapter to use: Belkin USB-C to Gigabit Ethernet Adapter - Apple. If you get the same error, the model is likely just not compatible.

It's still saying No Service for your cell signal. You need to get that issue fixed first before you can update your phone. You need both a WiFi and a working cell signal to do the updates.

If you see No Service or Searching on your iPhone or iPad

https://support.apple.com/en-us/HT201415

Click on the link l posted and follow the instructions

Contact your carrier for help with this. Once you get the ‘no service’ issue fixed, then try to update your phone.