Here is a UMI S1 Stock ROM Firmware which can be used to load and flash stock firmware on any UMI S1 of this exact variant. Any MTK Flash tools can download and flash this UMI S1 flash file on your S1 so long as that MTK Flash Tool supports MTK Scatter File.
Since most major software malfunctions on any MTK Android devices can only be corrected by flashing, this S1 flash file, if properly used, can unbrick (debrick) your S1 and also corrects any software issues your UMI S1 may currently have. Also, keep in mind that when you load stock firmware on your UMI S1 using any MTK flash tool, your UMI S1 will be reset to factory defaults settings and by that, definately, your UserData will be lost including contacts, messages and others.
Note: If your S1 is already bricked and you want to unbrick it, you will need to pay closer attention to the tutorials contained below here.
UMI S1 Stock ROM Firmware Download Link(s)
1. UMI S1_SC8901_V106_20130427 Stock Firmware Download Link
How to Flash Stock Firmware On UMI S1
1. Download your UMI S1 stock ROM firmware from the link above.
2. Extract the UMI S1 Firmware you downloaded from the link above onto a folder on your PC.
3. Download and install MTK android device drivers on your PC. You may skip this step if you have installed MTK drivers on your PC already otherwise, download MTK drivers here
4. Now, choose either of the tools listed below here to load the stock firmware on your UMI S1.
2. NCK Box
3. Miracle Box
See video tutorial here: How to Flash MTK Android Devices Video Tutorial
Note
1. Each of the tools listed above contained step by step guides with illustrated pictures on how to flash stock firmware on your UMI S1.
2. If your device is bricked already, I recommend that you use NCK Box or SP Flash. Both are the safest toolS for flashing MTK Android devices.
3. If you require any further assistance, simply drop your comment detailing the issue(s) and I shall help you revive your UMI S1, if need be.