Set mongodb's `maxIndexBuildMemoryUsageMegabytes` setting in conf file
The different approaches for configuring setParameter options (via runtime admin command, config file setting, or command-line option) are listed in the Synopsis section at the top of the MongoDB Server Parameters page you referenced.

You can use setParameter key/value pairs in the YAML configuration file.

For example:

setParameter:
    maxIndexBuildMemoryUsageMegabytes: 700


To confirm this setting has taken effect via the mongo shell, use either of:

// Check the parameter values parsed from config file or command-line options
db.serverCmdLineOpts().parsed.setParameter

// Check the current setting of the maxIndexBuildMemoryUsageMegabytes parameter 
db.adminCommand({getParameter: 1, maxIndexBuildMemoryUsageMegabytes: 1})