First, I download the XSD for the CDT from Appian. Then I open the XSD file and manually add the new fields. For example:

<xsd:element name="status" type="xsd:int">

<xsd:annotation>

<xsd:appinfo source="appian.jpa">@Column(name="REQUEST_STATUS_ID", nullable=false, columnDefinition="INT UNSIGNED") @JoinColumn(name="REQUEST_STATUS_ID")</xsd:appinfo>

</xsd:annotation>

</xsd:element>

<xsd:element name="isActive" nillable="true" type="xsd:boolean">

<xsd:annotation>

<xsd:appinfo source="appian.jpa">@Column(name="IS_ACTIVE", columnDefinition="BIT")</xsd:appinfo>

</xsd:annotation>

</xsd:element>

While adding the columns, I make sure that:

The name, @Column, and columnDefinition match exactly with the database table.
The data types in XSD and DB are aligned properly.
Any foreign key column includes the correct @JoinColumn.

After updating the XSD, I upload it back to the CDT in Appian.Once it is uploaded successfully, I validate and publish the corresponding Data Store to ensure everything maps correctly and no mismatches exist.