The Dell documentation lists the front panel jack as a Headphone jack.  No mention of microphone.  

If you want to use a microphone you will need a USB connected microphone (or headset mic combination).

Another option is to use an external USB connected sound card that is OS compatible and has the jack functions you want.

Dell OptiPlex 3050 Small form factor Quick Start Guide- Windows 10

I have new headset mic combination Logitech head set with mic 3.5mm pin . Head phones work but. It shows mic not plugged in 

The front panel jack is ONLY headset.  NOT a mic input.

So i cant use Mic in this 3050 sff . Can u help with the solution please

Don't believe anything you read about the front jack not being a TRRS headSET jack. I believe @fireberd means well but his help and this thread and another thread (https://www.dell.com/community/Optiplex-Desktops/3050-mic-not-working/td-p/6246246) is misleading at best. 

Go to devmgmt.msc, enable showing hidden devices, remove all Realtek audio drivers and check the box to uninstall (fully remove) the drivers. Reboot, let Windows automatically install some Microsoft default drivers, and then your headset microphone will work well.

The Dell drivers are faulty, I don't see another explanation. I have tried a clean install with the Dell audio drivers and could reproduce the non-working microphone behaviour.

There are two different wiring conventions for the mic on a TRRS connection.  I don't know which convention is used on this model.  One version the second ring is the "Hot" mic connection and Sleeve is ground.  The other version is exact opposite, the second ring is ground, and the Sleeve is the mic hot (signal) connection.