how to run 32-bit apps with update

If you mean in Catalina, you can't. You either have to update to a 64bit version of Excel or use a different app.

Microsoft Office 2016 (updated), Office 2019, and Office 365 all run with Catalina. 32 bit apps do not run with Catalina.

Look into the Free LibreOffice, it handles MS Office files…

https://www.libreoffice.org/

Apple macOS (Mac OS X)

The software and hardware prerequisites for installing on a Apple macOS computer are as follows:

• LibreOffice 6.3.x: macOS 10.10 (Yosemite) or higher

• LibreOffice 6.2.x: macOS 10.9 (Mavericks) or higher

• Intel processor

• 512 MB RAM

• Up to 800 MB available hard disk space

• 1024x768 graphic device with 256 colors (higher resolution recommended)

It is a recommended best practice to back-up your system and data before you remove or install software.

Notes:

• For certain features of the software - but not most - Java is required. Java is notably required for Base.

• Due to an issue, there are the following restrictions with Java: on macOS 10.10 and newer, JRE isn't found, JDK is required

• LibreOffice 4.3 can still run on OS X 10.6+, but please understand that this support ended when 4.3 was retired on May 27, 2015.

https://www.libreoffice.org/get-help/system-requirements/#Apple

Feature Comparison of LibreOffice v6.3 with Office 365/Office 2019 for Mac

https://wiki.documentfoundation.org/Feature_Comparison:_LibreOffice_-_Microsoft_Office