Hello kilsoo,
In order to export higher version of toolchain, you should follow these steps.
For example, assume you are using L4.19.35_1.1.0 BSP
1. Download documents for the version of linux BSP
Embedded Linux for i.MX Applications Processors | NXP

2. Setup environment of Yocto BSP
Follow steps in i.MX_Yocto_Project_User's_Guide.pdf to set up environment of Yocto BSP, and compile it successfully.
3. export the toolchain from Yocto BSP
Follow steps described on standalone operations in i.MX_Linux_User's_Guide.pdf to export toolchain, and install it to /opt directory.
see "4.5.12 How to build U-Boot and Kernel in standalone environment" of the document, please!
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if you want to get other version of toolchain, use the similar steps, please!
Hope these information is helpful to you.
Have a nice day!
B.R,
weidong