This requires bands 1, 2 and 3. Copy them to the local computer hard-drive.
First, import the Landsat GeoTIFF band files into ERDAS Imagine format.
Select Import (should be default setting)
Type: choose GeoTIFF
Media: File
Input File: Click on open folder and locate files on hardrive - select the first one to import
Output File: Select where you want the output file to be saved (usually same place)
Keep file names consistent, e.g., l71039036_03620000128_b10.tif becomes l71039036_03620000128_b10.img
Repeat the process for the other two files. The conversion will take a minute or two for each of the 3 files.
Select Utilities
Select Layer Stack...
Layer Selection and Stacking (new window appears):
Choose input file (click on open folder to locate .img file)
Click on Add button.
Choose second file to input.
Click on Add button.
Choose third file to input.
Click on Add button.
When all 3 files are listed in the window, then enter Output File name, e.g., l71039036_03620000128_b10.img and l71039036_03620000128_b20.img and l71039036_03620000128_b30.img become l71039036_03620000128_b321.img
It will take several minutes to process all 3 bands into one image.
Open this new combined image file.
Select Band Combinations and verify that the bands are indeed:
Band 1 = Blue
Band 2 = Green
Band 3 = Red
Finally, export the combined image file to GeoTIFF.
Select Export
Type: choose GeoTIFF
Media: File
Keep file name and location consistent, e.g., l71039036_03620000128_b321.tif