You can check for the following things to bring your hp printer from offline to online state:
Make sure that the printer is connected to the PC:
This is the first thing you need to check when your hp wireless printer offline.
For a connection to a USB printer
Turn off the printer by pressing the power button and wait 5 seconds.
Unplug the connected USB cable from the back of the device.
Switch on the printer. It might begin printing queued documents, so wait for it to complete that and turn silent prior to proceeding.
Wait and reconnect the cable to your printer for 5 seconds. Ensure that the cable sits securely on the printer's USB port while at it. If it starts printing, let it complete it before proceeding to the next step.
Retry printing. You're good to go if it does. If not, read on to learn how a wireless network can turn the printer online.
What does it mean the hp wireless printer offline?
When you try to print a document, sometimes a popup says the hp wireless printer offline. There are multiple reasons why your hp wireless printer offline. Some of the reasons why hp printer is poor USB or Internet Connectivity, outdated driver and faulty hardware. All these reasons can lead to a hp wireless printer offline.
Reset the Printer
Make sure the printer is inactive before proceeding. Unplug the power cord from the back when the device is switched on. Disconnect from the power outlet the same thing. Wait a minimum of 1 minute.
The power cord is reconnected to the power socket. Re-plug the power cord to your printer’s back.
To do so, press the power button if it does not switch on. Retry taking the printout once it turns on. If you can't, proceed to the next step.
Remove your printer and reinstall it:
Right-click the devices and printers printer and select "Remove device." Now add the printer again by selecting the Devices and Printers Add a Printer option.
This is some of the ways you can try to bring your Hp wireless printer offline to online
Let's see the reason which makes the hp wireless printer offline:
Driver issue: An obsolete printer driver may be a reason why the hp wireless printer offline. If the driver is outdated, the driver must be updated by the user. This can be done by visiting the website of the manufacturer. The support for HP printers can help you with this.
Poor USB connection: poor USB connectivity allows the computer to be disconnected from your printer. The HP printer displays offline when the printer is disconnected from the computer.
Internet problem: poor connection to the internet can also cause offline HP printer problems. If your connection to the Internet seems weak, reboot the router and check again to print.

If you are still unable to do so then you can reach our technical support team to assist you to solve your hp printer problem.
Reference Link: https://hpwirelessprinteroffline.weebly.com/